THE semaphorin/collapsin family of proteins comprises molecules thought to be important for the guidance of growing axons. All members of this family, which includes both secreted and cell-surface molecules, share a conserved domain of ∼500 amino acids. Here, we report the cloning of a novel murine semaphorin, termedM-sema IV. It displays 96.3% identity to the human semaphorinH-sema IVand is therefore likely to be the respective murine homologue. In addition, an isoform was identified, which contains an additional 31 amino acids in the semaphorin domain.M-sema IVappears to be expressed ubiquitously in adulthood. During embryo-genesis, in situ hybridization revealedM-sema IVexpression in subregions of the central nervous system and various other tissues like skin, kidney, lung and intestine.